Efficient methods of text entry are becoming increasingly important in today's mobile device market due to the continuous growth in use of SMS text messaging on mobile phones, the growing number of users that rely on Internet connection via cellphone to retrieve email on the go, the continued proliferation of mobile Internet connectivity devices, and the increasing portability of other types of text applications such as Chat, Instant Messaging (IM), Calendar, Address Book, Contacts, Word Processor, etc. Some devices have offered folding and/or plug-in keyboards that follow the standard Dvorak or, more commonly, the QWERTY keyboard layout familiar to users working on PCs, but these are awkward to carry or to use in mobile situations. If the keys are miniaturized to fit on the mobile device profile, the small individual keys become difficult to operate correctly and accurately. Each key requires its own footprint and switch, and the larger number of keys takes up valuable space on the device's printed circuit board and imposes commensurately greater tooling and assembly costs.
For many decades, there has been the long-used practice of imprinting the phone keypad's #2-#9 digit keys with 3 letters of the English (Latin) alphabet each (with a 4th letter from the infrequently used ‘Q’ and ‘Z’ characters added on two of the digit keys), so that a caller can “spell” a telephone number from a mnemonic word. With the advent of automated telephone exchange systems, it has become common to provide the function of automatic call routing by having the caller “spell” the name of the person being called using the keypad's digit keys corresponding to the letters of the name and predicting the correct name from a stored directory of names indexed to the various digit-key combinations. However, such predictive spelling systems often produce “false positives”, i.e., they select alternative words spelled by the same keypress combination that are not the ones intended by the user, or they require the user to take additional steps to select or input the correct word from among the candidates returned.
The predictive spelling approach has been more broadly adapted for text entry on phone keypads using the T9™ predictive spelling system of Tegic Corp., Seattle, Wash., which employs a stored dictionary of words indexed to their respective 10-digit keypress combinations and predicts which word is intended by the user by ranking the words for selection based on frequency of use. A further adaptation of the predictive spelling approach has been recently developed by Research In Motion (RIM) Corp., Montreal, Canada, in its SureType™ keyboard system for its Blackberry™ wireless PDAs in which two extra columns of four keys each are added on each side of the three columns of the standard 12-key configuration, and up to 2 alphabetic letters or symbols are assigned to each of the 15 keys to resemble a standard QWERTY 26-letter keyboard. By assigning two letters per key combined with predictive spelling, the SureType™ system allows an expanded range of keypress combinations to be input to select the intended word correctly with less “false-positives”. Other types of RIM keyboards have been devised with assignments of letter to keypad keys, e.g., as shown in PCT Published Patent Application WO02101531A1. However, these enhanced keypad layouts require additional tooling and assembly costs, and are still subject to the inaccuracies of predictive spelling.
Other systems have been developed to use the standard 12-key, 10-digit keypad to input text without using predictive spelling. In a commonly used multi-keypress keypad system, the user can select a letter to be input by pressing the digit key that has that letter in its imprinted set, then the user either pauses to allow the first letter in the set to be entered, or quickly enters one or more keypresses of the same digit key to select the second or subsequent letter in that set. A “mode” key, such as the “#” key, has also been used to switch between uppercase and lowercase letters and/or to symbol mode. However, the multi-keypress input method requires a relatively high number of keypresses per data entry (KPD), e.g., KPDs averaging 2.2 or more.
Another type of direct keypad entry system imprints up to 4 letters or symbols in radial directions around each digit key, and uses the 4-direction arrow keys or Radial Direction Indicator (RDI) cursor to select which letter or symbol is selected from the imprinted set. This system is more fully explained, for example, in U.S. Pat. No. 6,320,942 to Chang at el., assigned to KeyTouch Corp., Walnut, Calif. However, the KeyTouch RDI input system is not easy for the user to operate, since it requires a relatively high number of key presses per data entry (KPD), e.g., KPDs averaging 2 or more, and since it requires discerning which of the small imprinted characters or symbols are imprinted in which radial position, then selecting the corresponding RDI arrow key. Other attempts to provide for text entry on small mobile devices include voice recognition and stylus entry from an LCD display of either hand written text or of soft keys of a keyboard layout, but these have not operated reliably enough, are usually costly solutions, and/or are inconvenient to operate in mobile situations.